Field
The present invention relates generally to liquid-cooled heat sinks, and more particularly to liquid-cooled heat sinks for light emitting diode (LED) arrays.
Related Art
Semiconductor light sources, such as light-emitting diodes (LEDs), generate heat during their operation. In some high power light sources, hundreds of high power LED chips are arranged closely together in an LED array or matrix. The LEDs are attached to a substrate or ceramic body. In these high power light sources, a large amount of thermal power is dissipated. The amount of thermal power may be as high as 1000 W or greater. Since the performance and requirements of LEDs, including their brightness, color, optical output power, driving voltage, and life span, are temperature dependent, cooling the LEDs uniformly and homogeneously is advantageous, especially in high performance applications. For example, in some high performance applications, the temperature differences between the LEDs within the LED array should be less than 15 percent.
One method for cooling the LED array is to use a liquid, e.g., water, as a cooling medium. For example, as shown in FIG. 1A, a cooling liquid medium flows through a closed cooling liquid channel 110 inside the substrate or ceramic body 120 on which the LEDs (not shown in the figure) are mounted. The cooling liquid channel 110 may wind through the ceramic body 120 or branch out to different parts of the ceramic body 120 for cooling the ceramic body 120 and the LEDs mounted thereon. Because the cooling liquid medium absorbs heat from the ceramic body 120 as it enters the cooling liquid channel 110 from inlet 130 and exits through outlet 140, the temperature of the cooling liquid medium at outlet 140 is higher than that at inlet 130. Accordingly, as shown in FIG. 1B, a temperature gradient is developed across the ceramic body 120. For example, the temperature of the left-end portion 150 of the ceramic body 120 is higher than the temperature of the right-end portion 160 of the ceramic body 120. As a result, the LEDs (not shown in FIG. 1B) mounted on the ceramic body 120 have significantly different operating temperatures.
Other examples of cooling systems that have undesirable temperature gradients developed across the cooling systems include those disclosed in the U.S. Pat. No. 5,841,634 and the German patent DE 202 08 106 U1.